Add inbox, drafts, trash, templates, as well as tentative support for custom...

Add inbox, drafts, trash, templates, as well as tentative support for custom folders.  The collection names (as well as the names of the folders in the maildir) are hardcoded to English -- i18n will be handled with EntityDisplayAttributes.

svn path=/branches/kdepim/soc/kdepimlibs/; revision=985142